This invention relates to the preparation of extrudable and injection moldable compositions comprising submicron refractory hard metal powders such as silicon carbide and titanium diboride powders, and hydrocarbon plasticizers such as paraffin waxes and synthetic resins.
Techniques for forming refractory powders into shapes for sintering include the extrusion or injection molding of a blend of the refractory powder with a plasticizer which enables the blend to flow under heat and pressure. The quality of an article made by extrusion or injection molding depends in significant part upon the uniformity of the powder-plasticizer blend. Submicron powders, i.e., powders having particles predominantly under one micron in size, have a tendency to agglomerate. Consequently, they tend to resist dispersion in plasticizers such as molten wax. When such powders are added in a dry state to molten plasticizer, extended mixing periods may be required to work the powder uniformly into the plasticizer. However, even with extended mixing, uniform blending of the powder and the plasticizer may not be achieved.
U.S. Pat. No. 3,234,308 describes the blending of comminuted ceramic with organic binder (a) cold, in a ball mill, and (b) in a heated muller, the ceramic being added to melted organic binder and the resulting mixture being cooled. U.S. Pat. No. 3,422,173 describes preparing a blend of ferrite and a wax binder on a two-roll rubber mill. U.S. Pat. No. 2,593,507 describes mixing refractory powder and organic binder above the melting point of the binder in a heated mixer and also describes dissolving the organic binder in solvent, adding the refractory powder and mixing, and then heating to eliminate the solvent.